Fractionation system



March-21, 1967 F. E. JOHNSON ETAL FRAGTIONATION SYSTEM Filed Oct. 25,1964 ACCUMULATOR STEAM] 27 555% EE-E CHE STEAM STOVE OI L ST EAM ,i P BYTOPPED CRU DE DIESEL BASE GA L f S Ol INVENTORS F. E. JOHNSON M.F. POTTSA 7' TORNEVS very expensive and complex, treatments. 9

United States Patent 3,310,487 FRACTIONAT 0N SYSTEM Frank E. Johnson andMack F. Potts, llartlesville, Okla,

assignors to Phillips Petroleum Company, a corporation of Delaware FiledOct. 23, 1964, Ser. No. 405,973 8 Claims. (Cl. 208-355) This inventionrelates to process and apparatus for fractionation. In one of itsaspects, the invention relates to the treatment of intermediatedistillate fraction from fractionation by treating same in astripper-dehydrator zone employing a stripping medium and reducedpressure stripping while automatically controlling the flow ofdistillate to the stripper-dehydrator zone by means of a level sensingand control device in said stripper-dehydrator zone and operative on theinput line to said stripper-dehydrator zone. In another aspect, thisinvention relates to the control of the flow of intermediate distillatespassed to side strippers from a fractionation zoneresponsive to theliquid level in'each of the side strippers. In a further aspect, thisinvention relates to a unitary stripper-dehydrator apparatus comprisinga plurality of intercommunicating sections wherein stripped liquid fromone section is passed to another section responsive to liquid level inthe latter section.

Crude petroleum is madeup of hundreds of different individual componentsincluding natural gas and light gasoline, waxes and asphalts. Therefining of petroleum separates these multitudinous constituents intovarious fractions or phases according to properties such as boilingrange and viscosity, The separation of these many constituents intoseveral general fractions, i.e., light distillates (gasolines,kerosenes), intermediate distillates (heating or diesel base oils, gasoils), heavy distillates (lubricating base oils), and residues (pitch,asphalt), requires many Foremost among these treatments isfractionation, or, specifically, fractional distillation, wherein theabove-mentioned fractions and even specific constituents are separatedaccording to their boiling temperatures, heavier materials tending tocollect at the bottom of the fractionator and lighter materials tendingto collect at the top of the fractionator, and an infinite number ofvariations and blends of the two being, available at an infinite numberof locations between the top and the bottom of said fractionator. Anomnipresent problem of fractional distillation is the separation of apure and unadulterated fraction or constituent. The common result ofmost attempts to separate a particular fraction or a constituent is theobtention of a material composed substantially of the desired fractionor constituent, but also containing generally in unacceptable amounts,other fractions or constituents which not only are undesirable, but,also, must be removed prior to use and/or sale of the desired fractionor constituent.

This invention is concerned with solving, at least in part, theabove-mentioned problems and, at the same time, efiecting a moreeconomical, efiicient and complete recovery of all fractions andconstituents present in a crude oil, for example.

Accordingly, it is an object of this invention to provide process andapparatus for separating fractionable materials into their variouscomponent fractions.

Another object of this invention is to provide fractional distillationof a hydrocarbon oil by use of steam and reduced pressures.

Another object of this invention is to increase the amount of overheadhydrocarbon and intermediate hydrocarbon produced by a 'fractionatingsystem.

Another object of this invention is to increase the tendency of lighterhydrocarbons to separate from the heavier residuum and thereby produce acleaner separa- "ice tion of topped crude from intermediate and lightdistillates.

Other aspects, objects, and the several advantages of this invention areapparent from a study of this disclosure, the drawing, and the appendedclaims.

Although the illustrated embodiments of this inventionrefer to the useof a hydrocarbon oil, it is to be understood that this invention is notlimited to such oil, but is applicable to the distillation andfractionation of any distillable or fractionable material such as, forexample, vegetable, animal and mineral oils, and distillate organic andinorganic chemical mixtures or solutions. It is also to be understoodthat the drawing hereinafter described is diagrammatic and can bealtered in many respects by those skilled in the art in possession ofthis disclosure and yet remain within the intended scope of thisinvention.

In accordance with this invention, one or more distillate fractions orside streams removed from a fractionator are passed to agroup ofstrippers wherein the distillates are subjected to stripping both with afluid stripping medium and reduced pressure. In accordance with oneembodiment of the invention, a unitary, combined stripper-dehydratorcomprising a plurality of sections is provided for carrying out thestripping operation. Such an apparatus takes advantage of efficientutilization of heat exchange between strippers. Also, optimum strippingconditions can be selected to achieve the desired degree of separationwith minimum loss of bulk liquid, e.g., distillate subjected tostripping.

More specifically, according to the invention, the rate of flow ofdistillate material to be subjected to stripping conditions passed toone or more side strippers associated with a fractionator are controlledresponsive to the liquid level in side strippers receiving liquid to besubjected to stripping. Further, according to the invention, whenapplying the control of flow of distillate to be stripped in a verticalmulti-compartmented stripper, liquid re moved from one stripper andpassed to another is regulated responsive to the liquid level in thelatter section or compartment.

In a specific embodiment of the invention, a multicompartmented, orsectioned, substantially vertical stripper-dehydrator is providedwherein the sections are serially connected, and further, wherein steamstripping is employed in one section and vacuum or reduced pressure isemployed in a following section and, further, wherein the strippedvapors in the latter section are combined with the stripping medium inthe first section and these vapors are all recovered and returned to thefractionator for further recovery and separation. By so. operating,eflicient utilization of both the vacuum pro, ducing equipment and steamand fluid stripping medium is achieved.

As indicated above, the flow of liquid to the strippers is controlledresponsive to the level of liquid in a lower portion or base of eachstripper. The control means which senses :the level of liquid in thebottom of the stripper is opera-tively connected to a valve whichcontrols the amount of flow of intermediate distillates from thefractionator plates to the top of the stripper or from another stripper.This control means is adjustedlin such a manner that, for example, whenthe level within the stripper rises above a desired maximum, the levelcontroller will sense this variation and automatically adjust the valvehereinabove mentioned, thereby decreasing the amount of feed from thefractionator plate or previous stripper to the top of a succeedingstripper. A similar, but opposite, function is obtained when the liquidlevel in the stripper falls below an arbitrarily determined minimumlevel.

The above-mentioned stripper-dehydrator can be provided with internalbaffles or packing in order to obtain turbulence and/or large contactsurface area as desired. However, equally as satisfactory results can beachieved by removing and not using any type of internal bafiie in thestripper-dehydrator. The removal of baffles not only decreases the costof the apparatus and process, but also allows the use of astripper-dehydrator apparatus of significantly smaller overalldimensions. However, it is often preferred to utilize contact plates,e.g., perforated trays, in the strippers. It should also be noted herein relation to the above-described unitary stripper-dehydrator columnthat results are achieved by this single piece of apparatus whichheretofore generally required not only a stripper, but also a separatevacuum or flash dehydrator which acted on a bottom flow from thestripper to primarily flash away water and some lighter distillatevapors.

Referring now to the drawing, a crude oil feed introduced by way of lineis passed through heater or furnace 11 to preheat the feed, and theheated feed is then passed through line 12 and introduced into a lowerportion of fractionator '13. Fractionator 13 is provided with aplurality of spaced contact trays 15. Steam is intnodu-ced into the baseof fractionator 13 by way of line 14. A topped crude fraction is removedfrom the base of column 13 by way of line 16 and passed to furtherprocessing, e.g., vacuum distillation or other treatment as desired. Therate of flow of topped crude withdrawn from the bottom of column 13 iscontrolled responsive to flow controller 17, which operatively regulatesthe position of a control valve in line 16. Flow controller 17 isperiodically reset by the :liquid level in the bottom of column 13.

Gasoline boiling range materials and lighter are removed overhead fromcolumn 13 by Way of line 18 and passed through condenser 19 andcondensed liquid is collector in accumulator 20. Non-condensed gases areremoved from accumulator 20 by way of line 21. A portion of thecondensed liquid collected in accumulator 20 is returned to fractionator13 as reflux by way of line 23. The remainder of the gasoline product isremoved from accumulator 20 by way of line 22 for further processing asdesired.

At one or more intermediate positions along fractionator 13, varyingdegrees of lighter hydrocarbons are withdrawn and treated in sidestrippers, as set forth hereinbelow. An upper plate in fractionat-or 13is tapped by line 24 and carries a naphtha boiling range fraction tostripper 25. The rate of flow of naphtha passed to stripper 25 fromcolumn 13 by way of line 24 is regulated by valve 26 responsive to theliquid level in the bottom of stripper 25. Steam or other strippingmedium is introduced into the base of stripper 25 by way of line 27.Steam and light hydrocarbon vapors are removed overhead from stripper 25by way of line 28 and returned to fractionator 13 at a point above theliquid withdrawal for stripper 25. A bottom stream of stripped naphthais removed from stripper 25 by Way of line 29 for further processing asdesired.

In a lower portion of fractionator 13 a gas oil stream is removed fromfractionator 13 by way of line 30 and passed to stripper 31. The flow ofgas oil to stripper 31 is controlled 'by valve 32 responsive to theliquid level in the base of stripper 31. Steam or other stripping fluidis introduced into the base of stripper 31 by way of line 33, and anoverhead fraction comprising stripping medium and hydrocarbons lighterthan gas oil is removed from stripper 31 by way of line 34 and returnedto fractionator 13 at a point .above the liquid withdrawal for stripper31. A stripped gas oil stream is removed as bottoms from stripper 31 byway of line 35 for further processing as desired.

At an intermediate portion of fractionator 13 a side reflux loop isprovided wherein liquid is withdrawn from an intermediate tray by way ofline 36, passed through pump 37, cooler 38, and returned by Way of line39 to a point in column 13 above the liquid withdrawal. The rate ofcirculation of liqu'idt-hrough the loop is controlled by flow controller40.

According to one embodiment of the invention, a stove oil fraction isremoved by line 41 from an intermediate point in column 13 and passed tostripper-dehydrator 42 containing compartments 43, 44 and 45. The rateof flow of stove oil in line 41 passed to section 43 of column 42 iscontrolled by contnol valve 46 responsive to the liquid level in thebase of section 43 of stripper-dehydrator 42. Steam or other strip-pingmedium is introduced into the base of section 43 by way of lines 47 and48. An overhead stream comprising steam and lighter hydrocarbonmaterials is removed from section 43 and returned :to fractionator 13 byway of line 49 and introduced' into fractionator '13 at a point abovethe liquid withdrawal for line 41.

Stripped liquid collected in the base of section 43 is passed by way ofline 50 to an upper portion of section 44. The rate of liquidintroduction into section 44 is controlled by control valve 51responsive to the liquid level in the base of section 44. The liquidpassed to section 44 is subjected to reduced pressure or vacuumstripping by means of eductor 53, which removes vapors from an uppersection of section 44 by way of line 52. The light hydrocarbon vaporsremoved from the top of section 44 by means of eductor 53 are combinedwithsteam introduced into eductor 53 from line 47 and passed into alower portion of section 43 through line t8 along with stripping mediumbypassing eductor 53. Steam stripped and vacuum stripped stove oil isremoved from the base of section 44 of stripper 42 by way of line 54 forfurther processing as desired.

A diesel base distillate is removed from fraction ator 13 by way of line55 and passed through control valve 56 and introduced through spraynozzle 62 into an upper portion of section 45 of stripper-dehydrator 42.The rate of flow of diesel fuel passed to section 45 is con trolled bycontrol valve 56 responsive to the liquid level in the base of section45. Section 45 of stripper-dehydrator 42 is ordinarily subjected tovacuum stripper by means of eductor 58, which is supplied with steam bymeans of line 59. Light materials stripped from the diesel materialintroduced into section 45 are removed through line 60 and returned,along with steam used as vacuum producing medium, into fractionator 13by Way of line 61. If desired, steam can be introduced into the base ofsection 45 by means of line 57. Stripped diesel material is removed fromthe base of section 45 by means of line 62' for further processing asdesired.

As can be seen from the above description, a neat and compactstripper-dehydrator is provided whereby petroleum distillates can besubjected to both steam and vacuum stripping in the same vessel. Also,vapors from the intermediate section 44, which section is under vacuum,are passed together with the steam creating the vacuum in section 44 foruse as stripping medium in section 43. Moreover, heat from stream 62'(stripped disel base), for example, can be utilized for heat interchangeWith stream 54, or other streams as desired. Also, the compact,three-chambered apparatus described above provides efiicient utilizationof heat exchange by heat interchange between the separate vessels. Forexample, it will be observed that unit 44 is interposed between twoother chambers or strippers and that heat from bottom stripper 45 isavailable for heating stripper 44. Also, vapors from intermediatesection 44, which is under reduced pressure, are passed together withthe steam creating the reduced pressure for use as stripping medium intop stripper .43. Thus, the stripping medium in top stripper 43 consistsof oil, aswell as steam.

Example Crude oil at a temperature of about 720 F. and at contains 40spaced vapor-liquid contact trays. Steam is introduced into the base offractionator 13 below tray number 1. A topped crude fraction at atemperature of about 690 F. is removed from the base of column 13 by wayof line 16. The amount of topped crude removed in line 16 is 6,006b.p.s.d. A gasoline overhead fraction at a temperature of 338 F. iscooled, condensed, and collected in accumulator 20. A reflux stream isintroduced onto tray 40 (top tray) at the rate of 7,718 b.p.s.d. and agasoline product stream comprising 6,322 b.p.s.d. is recovered in line22 for further processing.

A naphtha stream is removed from trayGZ by way of line 24 and passed tostripper 25. Ordinarily, the naphtha stripper is not operated.

A gas oil stream is removed from tray by way of line 30 and is passed tostripper '31. gas oil stream of 2,352 b.p.s.d. is removed by way of line35. i

A stove oil stream is removed from tray 25 by line 41. and passed todehydrator-stripper 42 and introduced into the top of section 43. Steam(150 lb. steam) at the rate of 1,950 pounds per hour is introduced intosection 43 by line 47.- A steam stripped and vacuumstripped stove oilfraction at a temperature of about 435 F. is removed from the base ofsection 44 by line 54 at the rate of 3,718 b.p.s.d.

A gas oil stream is removed from fractionator 13 at tray 16 and passedto steam stripping section 45. Steam (150 lb. steam) at the rate of1,370 pounds per hour is introduced into vacuum producing means 58. Astripped diesel base stream at a temperature of about 560 F., and at therate of 2,604 b.p.s.d. is removed by line 62.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure, drawing and the appended claims to theinvention, the essence of which is apparatus and process are providedfor fractionation of. a fractionable material wherein at least oneintermediate distillate fraction is trapped out of a fractionator, fedto a unitary stripper-dehydrator having a plurality ofintercommunicating sections, the flow of intermediate distillate fromsaid fractionator to each stripper being controlled by a valve which isresponsive to the liquid level in each stripper, the overhead from thestrippers being returned to the fractionator and the underflow from eachstripper being passed for further treatment and, further, wherein anintermediate distillate is subjected serially to steam strippingfollowed by vacuum stripping and wherein vapors from the vacuumstripping are combined with the motive fluid :for steam stripping in thepreceding stripper.

We claim:

1. A method of fractionation comprising introducing a suitable feed intoa fractionator to produce, inter alia, intermediate distillates,removing at least one of said intermediate distillates from saidfractionator, passing said intermediate distillate to a combinedstripper-dehydrator zone divided into an upper section, an intermediatesection, and a lower section, contacting said distillate with astripping medium in said first section of said stripperdehydrator toproduce an overhead product, returning said overhead product to saidfractionator, subjecting a bottoms product removed from said firstsection to reduced pressure stripping in said intermediate sectiontopnoduce a second overhead product, combining said sec-- ond overheadproduct with the stripping medium utilized to produce said firstoverhead, recovering stripped liquid from said second section asproduct, passing a second intermediate distillate from saidfractionation to said. lower section and therein subjecting same tostripping, returning stripped overhead to said fractionation, andrecovering a second stripped product from the base of said lowersection.

2. A method according to claim 1 wherein the rate: of flow of liquid toeach of said sections is controlled responsive to the level of liquid ineach of said sections,

A steam stripped 3. A method for fractionating a crude oil feed in asingle fractionator into a plurality of distillate components whichcomprises passing same to said fractionator and subjecting same todistillation in the presence of steam, removing a topped crude fractionas bottoms from said fractionator, recovering overhead a gasolineboiling range material, condensing and collecting condensed material andreturning a portion as reflux to said fractionator and recovering theremainder as product, passing a gas oil fraction to a side stripperresponsive to liquid level in said stripper and subjecting same to steamstripping, returning an overhead fraction from said stripper to saidfractionation at a point above the liquid withdrawal for said stripperproducing a stripped gas oil fraction as bottoms from said stripperfraction, passing an intermediate stove oil fraction to a combinedstripper-dehydrator having an upper section, an intermediate section anda lower section, controlling the rate of flow of stove oil fractionpassed to said upper section responsive to the level of liquid in saidupper section, subjecting said stove oil fraction to steam stripping insaid upper section, passing steam stripped stove oil to saidintermediate section and therein subjecting same to reduced pressurestripping, combining overhead removed from said reduced pressurestripping with steam passed to said upper section, recovering steam andpressure reduced stripped stove oil from the base of said intermediatesection, and passing a diesel fuel from said fractionator to said lowersection and therein subjecting same to stripping, and recoveringstripped diesel base from the bottom of said lower section.

4. A multi-sectioned unitary stripper vessel comprising, in combination,an upper enclosed section, means to pass feed to said upper section,means to control the fiow of feed to said upper section responsive tothe level of liquid in said upper section, means to remove overheadvapors from an upper portion of said upper section, means to introduce astripping medium into a lower portion of said upper section, means toremove liquid from the bottom of said upper section and pass same tosecond section of said stripper, means to control the rate of liquidpassed from said upper section to said second section responsive toliquid level in said second section, steam eductor means to reduce thepressure in said second section, means for removing stripped vapors fromsaid second section and combining same with said steam in said eductorand passing said combined stream into the base of said upper section,and means for removing liquid from the base of said second section.

5. The apparatus of claim 4 which includes a lower section incombination with said upper section and said second section which isprovided with means for passing a feed to the upper portion of saidlower section, means to control the rate of flow of feed to said lowersection responsive to liquid. level in the base of said lower section,means to produce a reduced pressure in said lower section and meansconnected therewith for removing stripped vapors from said lowersection, and means for removing stripped liquid from the base of saidlower section.

6. The apparatus of claim 5 which includes, in cornbination, afractionator, means for passing a feed to be separated into a pluralityof components to said fractionator, means for removing a liquid bottomsstream from the base of said fractionator, means for taking an overheadstream from the top of said fractionator, condensing same, collectingsame, and returning a ortion of the condensed overhead as reflux to saidfractionator and recovering the remainder of said overhead as product,means connecting an intermediate portion of said fractionator with saidupper section of said stripper for passing feed to said upper section,said fractionator also being connected at a point above said liquidwithdrawal to the overhead vapor removal means connected to said uppersection, means in a lower section of said fractionator connected to saidlower section of said stripper for passing feed to said lower section,and means connecting said lower section with said pressure reducingmeans to return vapors to said fractionator.

7. The method of claim 3 further comprising reducing the pressure insaid lower section by steam reduction, withdrawing vapor as overheadfrom said lower section, admixing said vapor with said steam andreturning the admixture thus formed to said fractionator.

8. Means for separating hydrocarbons which includes in combination afractionator, means for passing a feed to be separated into a pluralityof components to said fractionator, means for removing a liquid bottomsstream from the base of said fractionator, means for taking an overheadstream from the top of said fractionator, condensing same, collectingsame, and returning a portion of the condensed overhead as reflux tosaid fractionator, and recovering the remainder of said overhead asproduct, multi-sectioned unitary stripper vessel means comprising incombination an upper enclosed section, means to pass feed to said uppersection from an intermediate section in said fractionator, means tocontrol the flow of feed to said upper section responsive to the levelof liquid in said upper section, means to remove overhead vapors from anupper portion of said upper section and pass said overhead vapors tosaid fractionator at an elevation above said intermediate section, meansto introduce a stripping medium into a lower portion of said uppersection, means to remove liquid from the bottom of said upper sectionand pass same to said second section of said stripper, means to controlthe rate of liquid passed from said upper section to said second sectionresponsive to fluid level in said second section, steam eductor means toreduce the pressure in said second section, means for removing strippedvapors from said second section and combining same with said steam insaid last eductor and passing said combined stream into the base of saidupper section, means for removing liquid from the base of said secondsection, a lower section in combination with said upper section and saidsecond section which is provided with means for passing a feed from saidfractionator at a point below said intermediate point to the upperportion of said lower section, means to control the rate of flow of feedto said lower section responsive to the liquid level in the base of saidlower section, steam eductor means to produce a reduced pressure in thesaid lower section, and means connected therewith for removing strippedvapors from said lower section and mixing said stripped vapors with saidsteam in said eductor, means for passing the mixture of said steam andsaid stripped vapors thus formed to said fractionator, and means forremoving stripped liquid from the base of said lower section.

References Cited by the Examiner UNITED STATES PATENTS 2,073,446 3/1937Ellsberg 208357 2,151,310 3/1939 Aldrich et al 208-355 2,240,752 5/1941Bogart et al. 203 2,321,826 6/1943 Kraft et al. 208355 2,640,013 5/1953Wilton 208-355 FOREIGN PATENTS 398,099 9/1933 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

H. LEVINE, Assistant Examiner.

1. A METHOD OF FRACTIONATION COMPRISING INTRODUCING A SUITABLE FEED INTOA FRACTIONATOR TO PRODUCE, INTER ALIA, INTERMEDIATE DISTILLATES,REMOVING AT LEAST ONE OF SAID INTERMEDIATE DISTILLATES FROM SAIDFRACTIONATOR, PASSING SAID INTERMEDIATE DISTILLATE TO A COMBINEDSTRIPPER-DEHYDRATOR ZONE DIVIDED INTO AN UPPER SECTION, AN INTERMEDIATESECTION, AND A LOWER SECTION, CONTACTING SAID DISTILLATE WITH ASTRIPPING MEDIUM IN SAID FIRST SECTION OF SAID STRIPPERDEHYDRATOR TOPRODUCE AN OVERHEAD PRODUCT, RETURNING SAID OVERHEAD PRODUCT TO SAIDFRACTIONATOR, SUBJECTING A BOTTOMS PRODUCT REMOVED FROM SAID FIRSTSECTION TO REDUCED PRESSURE STRIPPING IN SAID INTERMEDIATE SECTION TOPRODUCE A SECOND OVERHEAD PRODUCT, COMBINING SAID SECOND OVERHEADPRODUCT WITH THE STRIPPING MEDIUM UTILIZED TO PRODUCE SAID FIRSTOVERHEAD, RECOVERING STRIPPED LIQUID FROM SAID SECOND SECTION ASPRODUCT, PASSING A SECOND INTERMEDIATE DISTILLATE FROM SAIDFRACTIONATION TO SAID LOWER SECTION AND THEREIN SUBJECTING SAME TOSTRIPPING, RETURNING STRIPPED OVERHEAD TO SAID FRACTIONATION, ANDRECOVERING A SECOND STRIPPED PRODUCT FROM THE BASE OF SAID LOWERSECTION.